1. Field of the Invention
This invention relates to a continuous photography system, and more particularly to a motor drive unit which cooperates with a photographic camera to enable continuous photography.
2. Description of the Prior Art
So-called motor drive units which, by being mounted on a camera, detect the wind-up starting signal on the camera side after shutter release and automatically wind up the film are known. Also, along with the recent systematization of cameras, a motor drive unit usable in common with a plurality of types of cameras has been put into practical use. Where such motor drive unit is used with a plurality of types of cameras, the following problems arise.
A first problem is as follows.
Where a camera containing a flash unit therein is operated for continuous photography by the motor drive unit, it is necessary to provide photographing intervals of a predetermined value or greater, that is, to keep the frame speed (the number of frames photographed per unit time) of continuous photography below a predetermined value, relative to the flashlight emission preparation time, and more specifically the charging time of the main capacitor thereof. The frame speed differs depending on the time lag from completion of exposure until initiation of wind-up, the time lag from completion of wind-up until initiation of release and the power of the wind-up motor itself. In any case, however, in a motor drive unit capable of being mounted on a camera in which the photographing frame speed must be kept low, as in a camera containing a flash unit therein; and a camera in which the photographing frame speed need not be kept low, if the frame speed is adjusted to the former camera, it will become a low speed unnecessary to the latter camera and in the converse case, when the motor drive unit is mounted on the former camera, proper photography will become impossible.
Here, referring for example to the time lag from completion of exposure until initiation of wind-up, the wind-up starting signal on the camera side for operating the motor drive unit is produced by operating a switch by the operation of the rearward shutter curtain or, in the case of a single lens reflex camera, by the downward movement of the mirror after completion of exposure, and there is a time lag until actually film advance operation actually becomes possible after such signal has been produced. Thus, in anticipation of such time lag, it is necessary to provide in the motor drive unit a delay circuit which produces a certain delay time.
However, where it is desired to use such motor drive unit with other types of camera, if means producing the wind-up starting signal and the operating time of the rearward shutter curtain or the mirror differ from camera to camera, the time required from the production of the wind-up starting signal until completion of the photographing operation will also necessarily differ. Where there is a difference in length between time lags, the delay circuit must be adjusted to a camera having a longer time lag. In that case, a camera having a shorter time lag will have a useless delay time corresponding thereto and if an attempt is made to effect continuous photography with such camera combined with the motor drive unit, the frame speed during the continuous photography will be checked to an unnecessarily low value.
To overcome such demerit, it would occur to mind to set all cameras capable of using the same motor drive unit to the same time lag. However, this would remarkably hamper the degree of freedom of design of both the wind-up starting signal producing system and the subsequent operating system, and it is not desirable.